Conjugated polymer based light-emitting devices have become a topic of great interest since the report of electroluminescent properties in poly(phenylene vinylene) (PPV). A large variety of polymers, copolymers, and their derivatives have been shown to exhibit electroluminescent properties. The configurations of these devices may consist of a simple single layer, bilayers, or blends used to enhance efficiency and tune the emission wavelength, or multilayers that may allow the device to operated under an applied voltage. Typical single layer polymer LEDs are constructed by sandwiching a thin layer of luminescent conjugated polymer between two electrodes, an anode and a cathode, where at least one electrode is either transparent or semi-transparent.
Trivalent erbium ions in different host environments emit photons at several wavelengths, for instance, green emission at 545 nm, and infrared emission at 1.54 and 2.94 microns. This green emission has attracted attention for applications such as fabrication of electroluminescent (EL) devices for use in display technologies. The infrared emission at 1.54 microns is of high interest for optical communication, as this wavelength coincides with the minimum-loss transmission window of silica-based fibers, and the narrow line width of this emission at room temperature also offers high bandwidth capacity in fiber optical communication. Recently, erbium-doped silicon has become a very active field of research for its possible use as electrically pumped light emitters for 1.54 micron wavelength devices. The light emitting devices are based on erbium-doped inorganic materials and prepared by ion implantation, molecular beam epitaxy (MBE), or ion beam epitaxy (IBE) methods. Sharp electroluminescence is observed for these devices at room temperature. Trivalent neodymium and trivalent holmium, when excited, also emit at infrared wavelengths.
Rapid progress has been made in the field of organic EL devices ever since efficient electroluminescence was demonstrated from organic molecular materials. Organic fabrication techniques provide simple and easy methods to construct EL devices with high efficiency and low operating voltages. A variety of organic materials including metal complexes, polymers, and fluorescent dyes have been employed to the fabrication demonstrating different emission colors in the visible wavelength region. Among them, metal complexes such as aluminum tris(8-hydroxyquinoline) are widely used as emitting materials in sublimed molecular film-based EL devices. When coordinated with rare-earth ions, metal complexes exhibit extremely sharp EL emission bands due to the 4f electrons of the ions. Since 4f orbitals are effectively shielded from the influence of external forces by the overlying 5s2 and 5p6 orbitals, the states arising from the fn configurations are split by external fields by only about 100 cm−1. Moreover, as the central metal ions are excited via intramolecular energy transfer (IMET) from the triplet excited states of the ligand, the EL devices based on metal complexes can be very efficient in principle due to the contribution of triplet states.
It is thus an object of the present invention to develop a cheap, simple electroluminescent or photoluminescent device that demonstrates peak infrared emissions at room temperature.
Although described with respect to the field of light-emitting devices driven by an electric field or optical source, it will be appreciated that similar advantages of infrared emission, as well as other advantages, may be obtained in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.